LONDON -- Hundreds of London commuters were trapped for two hours Thursday when an underground train derailed.

Seven-hundred people were taken off the derailed subway and another that was behind it after they had waited for two hours, officials with Transport for London told the BBC.

The central London derailment was apparently caused by stored material in the tunnel that fell onto the track.

"Our initial reports suggest that a bale of material became dislodged from its licensed storage position in a tunnelcross-passage," a Metronet spokesman told the BBC.

About 20 minor injuries were reported.

Passenger Chris Christofi, who was aboard the train that derailed, said riders feared a bomb had exploded.

"We felt a massive jolt underneath the train which caused the train to move up and down and sideways," Christofi told the BBC. "There were some windows that seemed to blow in and explode and there was some soot that came into the carriage."

The incident occurred on the westbound Central Line between Mile End and Bethnal Green stations at about 9 a.m.